In order to make a dimensionally accurate rigid body from a mass of powder or other compressible workpiece, for instance formed of a powder-containing paste, a so-called powder press is used. At its most basic such a press 1′ has as shown in FIG. 1 a base 2′ holding a hard-metal sleeve 3′ having a cylindrical inner surface 4′ forming a cavity open in at least one direction P′, and at least one piston 5′ shiftable in the direction P′ into the cavity for compacting a mass 15 therein.
By means of a press of this type, it is possible to fabricate shaped workpieces made of metal powder by pressing and subsequent sintering. The use of a piston compressing powder that is introduced into a mold by an axial pressing movement for pressing powder is known. To this end, at least one piston 5′ is required that is inserted into the mold. In this case, the mold has a cavity that is opened toward the piston. The mold opening is closed by the piston except for a small clearance. The piston builds up the pressure required for the compression when inserted into the mold cavity.
It is also possible that multiple pistons 5′ are provided that can move in one axial direction P′. In this system the pistons 5′ can fit into a mold that is axially closed at one side or come from both axial directions in the case of a mold that is axially open in both directions, as shown in FIG. 1. In certain cases, throughgoing mandrel bars that do not primarily fulfill a compression function but rather a displacement function are used. The pistons can also fit laterally into the mold for generating undercuts or other geometrical forms. For removing the shaped workpiece, these pistons that fit in radially are pulled back so that the finished workpiece can be knocked out of the mold.
Generally, the mold consists of a mold base or ring and a mold sleeve inserted thereinto, or respectively sleeve, having the shape of the work piece. A powder press is known from the US 2002/0044985 of Nordell in which there is a press-out portion such that the mold walls that support the press-out channel are increasingly thinner. Due to the thin walls in this area, an increasing flexibility of the tool is achieved that facilitates workpiece removal.
According to the DE 198 30 601 of Hess, a press for powder and granulated material is provided in which two molds whose front faces define the shape of the shaped workpiece enclose an acute angle by means of guides. The surfaces of the front faces of the molds directly abut each other when the final shape of the shaped workpiece is reached.
For fabricating shaped workpieces having an undercut as seen in removal direction of the shaped workpiece a press having a mold and multiple pistons is known from the DE 195 08 952 of Zirkel. Here a segment pusher is used that can be moved also during the pressing operation for the shaped workpiece after the closing of the mold by means of advance and pull-back devices.
For generating the pressing power impacting upon the pistons themselves, it is known from the U.S. Pat. No. 6,539,853 of Hess to provide a device in which a hydraulic element interacts with a piezoactuator for achieving a compact design.
It is generally desirable to achieve a high functionality and variability by means of tool parts that can be moved relative to each other. In this way degrees of freedom in the fabrication of differently shaped workpieces are achieved. Contrary thereto is however the demand for a design of the device that is to be as compact as possible. Each additional press axis required a considerable increase of the tool installation space in the press. Therefore, a retrofitting of existing presses is not possible in most cases.